1. Field of the Invention
The present invention relates to fuel reforming apparatuses and fuel cell systems including the same. More particularly, the invention is directed to a reformer for a fuel cell, in which a reforming gas is generated in a partial oxidation reaction or an auto-thermal reforming reaction of a fuel.
2. Description of the Related Art
As is well known, a fuel cell is an electricity generating system for generating electrical energy using a fuel and an oxidant gas. The fuel cell may be either a polymer electrolyte membrane fuel cell or a direct oxidation membrane fuel cell.
A polymer electrolyte membrane fuel cell receives a reforming gas (generated in a reforming apparatus) and an oxidant gas that is different from the reforming gas. The polymer electrolyte membrane fuel cell thus generates electrical energy by an oxidation reaction of hydrogen contained in the reforming gas and an electrochemical reaction of oxygen contained in the oxidant gas.
The fuel reforming apparatus has a structure in which the reforming gas (rich in hydrogen) is generated in a steam reforming (SR) reaction, a partial oxidation (POX) reaction, or an auto-thermal reforming (ATR) reaction of a fuel by the use of a catalyst.
The SR reaction yields relatively high hydrogen production as well as stability. However, high heat energy has to be externally provided since the SR reaction is an endothermic reaction requiring a large amount of heat. Furthermore, in terms of chemical equilibrium, the apparatus increases in size due to a limited conversion rate and a low reaction speed.
The POX reaction is a sort of exothermic reaction. Thus, in comparison with the SR reaction, heat supply is decreased and reaction speed is increased, thereby permitting a small-sized apparatus with a high conversion rate.
The ATR reaction is a reaction in which the SR and POX reactions of the fuel simultaneously occur, resulting in a fast reaction speed and response.
In a conventional fuel reforming apparatus, when a reforming gas is generated by a POX reaction or an ATR reaction of a fuel by the use of a catalyst, the catalyst generates heat having a temperature of approximately 700° C. or greater. As a result, a hot-spot phenomenon occurs in conventional fuel reforming apparatuses. The hot-spot phenomenon is a phenomenon in which heat generated by a catalyst is concentrated on the interior wall of a reactor made of a metal material. The interior wall is thus easily oxidized and coke is formed inside the reactor due to oxide particles.
Accordingly, in conventional fuel reforming apparatuses reactants containing fuel cannot be smoothly transferred since the coke is formed when the interior wall of the reactor is oxidized due to the hot-spot phenomenon. In addition, catalyst reaction efficiency deteriorates, and durability and reliability of the entire apparatus are degraded.
The information disclosed in this Background section is presented only as background information on the invention, and may contain information that is not prior art or that is already known to a person of ordinary skill in the art.